A common method of digital video compression is to record the changes between frames. Thus, in a scene where little movement takes place a minimal amount of data is encoded. This is accomplished by encoding key frames and delta frames. A key frame corresponds to a whole frame which the video player can use as a reference and start point. A delta frame corresponds to change between a first frame and a subsequent frame. The decoding of the key frame and subsequent delta frame produces the un-encoded subsequent frame.
Frames are divided into multiple blocks representing regions. In sequential frames these blocks are analyzed for change. If a change exists, the data is encoded. If the data in the region is identical to the preceding frame, the data is redundant and need not be encoded. In this way, a minimal set of data is encoded from one frame to the next.
However, while this compression method was useful, it did not allow for a user to access a point in the digital video represented by a delta frame, for that frame can only be reconstructed using the preceding delta frames and key frame. While some advanced video players were able to retrace the initial key frame and preceding delta frames to eventually reconstruct the desired frame, most digital video players were unable to reconstruct the desired video frame in a timely manner. Therefore, key frames were periodically inserted into the digital video data. Thus, when a user desired to access a point in the digital video represented by a delta frame, the decoder merely need look back to the last key frame to reconstruct the desired frame. Having these key frames inserted, for example, every fifth frame, allowed for a user to access the digital video from either the closest key frame or a delta frame with a relatively short reconstruction time.
Generally, most of today's digital video data is encoded in the latter format, with key frames inserted periodically to serve as marker points. Key frames contain a relatively high amount of data compared to delta frames. Accordingly, the latter encoding process, which contains multiple key frames, has a much lower compression rate and uses a much larger bandwidth than the original coding process which contained one key frame.
While the latter encoding process provides the ability to manipulate the starting point of the digital video, a greater compression rate is sometimes desirable in certain situations, even at the cost of this ability. For example, when an administrator wishes to broadcast digital video to one or multiple clients a minimal use of bandwidth is desired. Transmitting the digital video data encoded with frequent periodic key frames is not desirable when a minimal bandwidth is desired. Therefore, there is a need to compress digital video data encoded without frequent periodic key frames.
A system according to invention principles address these deficiencies and associated problems.